Various thermal transfer recording methods are known in the art. Among them, a thermal dye sublimation transfer recording method is utilized as information recording means in various fields. In the thermal dye sublimation transfer recording method, a thermal transfer sheet comprising a dye layer containing a sublimable dye provided on a support such as a polyester film is heated by a heating medium such as a thermal head or a laser beam to form a dye image on an object. According to this method, a large number of color dots of three or four colors can be transferred by heating in a very short time onto an object, on which an image is to be recorded, to reproduce a full color image of an original. Further, since the formed image is very sharp and highly transparent, the reproduction of intermediate colors and the gradation are excellent and, thus, high-quality images comparable to the quality of full-color photographic images can be formed.
In the above method, however, objects, on which an image can be formed, are disadvantageously limited to dyeable plastic sheets or objects on which a dye-receptive layer colorable with a dye has been previously provided, and an image cannot be directly formed, for example, on metal plates or glasses, not to mention on ordinary paper.
In order to solve this problem, a receptive layer transfer sheet for the formation of a dye-receptive layer on an object has been used. In this dye-receptive layer transfer sheet, a dye-receptive layer is provided separably on a substrate, and a desired region of the dye-receptive layer transfer sheet is heated by a thermal head or the like from the backside of the sheet to transfer the dye-receptive layer onto an object in its necessary area only. A dye image can be formed on the object with the dye-receptive layer formed thereon.
In the receptive layer used in a dye-receptive layer transfer sheet in conventional thermal dye sublimation transfer materials, it is difficult to simultaneously realize both the adhesion of the dye-receptive layer onto the object and the releasability of a print from a thermal transfer sheet having a dye layer at the time of printing of an image, using the thermal transfer sheet, on the object with the dye-receptive layer transferred thereon from the dye-receptive layer transfer sheet. At the present time, importance is attached to ensure satisfactory adhesion, and, consequently, the releasability is disadvantageously unsatisfactory.
In order to ensure the releasability of the surface portion of the dye-receptive layer which has been transferred onto the object, a release agent (a silicone) should be localized around the interface of separation of the dye-receptive layer. In general, however, in the preparation of the dye-receptive layer transfer sheet, the release agent is localized at the interface of the dye receptive layer and the adhesive layer, which interface is opposite to the interface of separation of the dye-receptive layer.
When the amount of the silicone added is small, the adhesion of the dye-receptive layer to the object is ensured, but on the other hand, the releasability of a print from a thermal transfer sheet having a dye layer upon printing of an image, using the thermal transfer sheet, on the object with the receptive layer which has been transferred thereon from the dye-receptive layer transfer sheet is unsatisfactory. On the other hand, when the amount of silicone added is large, the adhesion of the transferred dye-receptive layer to the object cannot be ensured although the releasability at the time of printing can be developed. In order to ensure the adhesion of the adhesive layer overlying the dye-receptive layer in the dye-receptive layer transfer sheet, the amount of silicone added to the dye-receptive layer should be limited. This poses a problem that, at the time of printing using a thermal transfer sheet having a dye layer, the separability of the print from the thermal transfer sheet is unsatisfactory.
Accordingly, the realization of a transferable dye-receptive layer, which can realize the regulation of the state of presence of a release agent typified by silicones in the dye-receptive layer to provide satisfactory releasability from a thermal transfer sheet having a dye layer and adhesion to an object, has been desired.
Further, in the prior art technique, due to unsatisfactory adhesion of the receptive layer, which has been transferred onto an object, to the object, folding and/or heat expansion or contraction of the object in the image formed object have disadvantageously resulted in the separation of the receptive layer or breaking of the formed image. Under the above circumstances, the preparation of image formed objects (prints), which have high-density and high-definition photograph-like full-color images and possess excellent thermal properties, in an on-demand manner has been desired.